1. Field of the Invention
The present invention relates to a swash plate type compressor for use in an air-conditioning system for vehicles, and in particular, to an improved structure of a shoe-and-socket joint between a swash plate and a piston of a swash plate type compressor for providing sliding contact surfaces of the shoe and the socket of the piston with a better lubrication by the oil-contained refrigerant.
2. Description of the Related Art
A typical swash plate type compressor is disclosed in, for example, U.S. Pat. No. 4,329,913 of Nakayama et al. The compressor has a pair of horizontally axially aligned cylinder blocks which form a combined cylinder block. Axially extending cylinder bores and a swash plate chamber receiving a swash plate therein are formed inside the combined block, and the combined cylinder block is closed at both ends by front and rear housings, via valve plates. A drive shaft passes through the center of the combined block, and is rotatably supported by suitable radial and thrust bearing. The swash plate is fixed at the middle of the drive shaft and is operatively connected, via ball bearings and shoes, to double-headed pistons slidably fitted in the cylinder bores. Thus, the rotating motion of the swash plate within the swash plate chamber causes the reciprocal compression and suction motions of the pistons within the cylinder bores. The front and rear housings are provided with refrigerant suction chambers and refrigerant discharge chambers, which are interconnected with the cylinder bores and are connectable to an outside air-conditioning system by appropriate refrigerant flow pipelines. In other conventional types of swash plate, for example, as disclosed in the pending U.S. patent application Ser. No. 897,550, filed on Aug. 15, 1986, by M. Kato et al, and assigned to the same assignee as the present application, the ball bearings and shoes are replaced with semi-spherical shoes having a spherical contact face arranged in sliding contact with a spherical socket formed in the piston and a flattened contact face opposite to the spherical contact face and in sliding contact with the face of the swash plate.
However, in the above-mentioned conventional swash plate type compressor, the spherical socket of the piston is designed and formed to have substantially the same diameter as that of the ball or spherical face of the semi-spherical shoe, so that a complementary engagement is established between the piston and the ball or semi-spherical shoe. That is, there is almost no clearance between the piston and the ball or semi-spherical shoe. This makes it difficult for the oil-contained refrigerant in the swash plate chamber to flow between the spherical socket of the piston and the ball or semi-spherical shoe, and as a result, a lack of lubrication occurs in the sliding contact surfaces of the ball or semi-spherical shoe and the spherical socket of the piston. Thus, in a long operation of the swash plate type compressor, an abrasion of the both sliding contact surfaces, and in particular, the abrasion at the outer edge of the spherical socket of the piston, occurs. Accordingly, the clearance between the spherical socket of the piston and the ball or semi-spherical shoe increases. Due to this increased clearance, noise is generated by the ball or shoe striking the socket. Further, burning-in between the socket and the ball or shoe occurs due to a relative fast sliding contact.